If I’m thin then I’m healthy, right? Wrong. There are several misconceptions people have about weight, losing it and what’s healthy. Here’s the low-down on some myths we’re better off busting.

Kids have to lose weight to shed obesity: As children grow, they put on weight, but how much is normal, and how much is excessive and potentially a hazard to their health? In the latest study, published in the journal Lancet, researchers from the National Institute of Diabetes and Digestive and Kidney Diseases at the National Institutes of Health developed a mathematical model to differentiate between healthy weight gain and the extra pounds that contribute to obesity. The model takes advantage of more accurate assessments of how many calories heavier children take in, as well as how quickly and efficiently they burn off those calories, and the ratio of fat to muscle in their bodies. The resulting model shows some kids can outgrow their obesity around puberty even if they don’t lose weight. That’s because obesity is a measure of not just weight but the ratio of height to weight known as the body mass index (BMI), and as children grow, they transform fat into muscle, which can weigh as much, if not more than fat tissue. So kids with a high BMI that might suggest obesity may not actually be overweight.

Still, the researchers say that teaching children about portion control and balancing what they eat with physical activity to burn off excess calories are important lessons to learn early.

You can’t be fat and still be fit: A person’s level of physical fitness, as well as his weight, matters for overall health. A study in 2012 showed that overweight and obese people were at no greater risk of developing or dying from heart disease or cancer compared to normal weight people, but only if they were as metabolically fit as their slimmer counterparts. When it comes to premature death, it’s less about how much fat a person carries, but what kind of fat. Visceral or belly fat, for example, is considered more metabolically harmful than fat that sits just under the surface of the skin. Visceral fat, which is embedded more deeply within muscles and organs like the liver, release agents that can disturb the body’s energy balance, shunting calories into fat. Lean people can have high levels of visceral fat in their tissues, while overweight individuals may be carrying more subcutaneous fat and therefore could even be metabolically fitter than those who are slimmer.

Most people who put on weight, however, don’t enjoy a fit status for long. Eventually, the excess weight can contribute to higher rates of high blood pressure, diabetes, and heart disease.

You can eat what you want and just exercise to lose weight: Cutting calories by adjusting what you eat is actually the most effective way to lose weight. Ideally, consuming fewer calories and exercising is a more efficient way of dropping pounds, but for most people, passing up the chips is easier than sweating it out on a treadmill for an hour. Downing 140 calories from a can of soda, for example, takes only a few minutes, but would take half an hour of moderately intense walking to burn off. “You can greatly undermine weight loss efforts and general health by not considering the quality of the foods you eat. It is important to consider calorie density and nutrient density of foods to maximize exercise performance and improve health status,” says Gayl Canfield, the director of nutrition at Pritikin Longevity Center.

Long bouts of low-intensity exercise are best for losing weight: Fitness experts are trying to de-bunk the myth that pounds melt off faster with low-intensity aerobic exercise than higher intensity workouts. “It’s true the body burns proportionally more fat calories than carbohydrate calories at a lower training intensity, however, should you increase your exercise intensity into the cardiovascular zone you will burn more overall calories,” says Scott Danberg, the director of fitness at Pritikin Longevity Center. Mixing in some short bouts of high-intensity exercise can translate into benefits on the scale.

Eating protein is the best way to feel full and keep calories in check: Lean protein is indeed a good way to get filled up, but fiber is even better, because it comes with fewer calories. To make sure you’re not feeling hungry but still getting all your nutrients, load your plate with fruit, vegetables beans and grains.